Multi-hop reflector sessions

ABSTRACT

A method for measuring and reporting performance parameters in a network having at least one originator for generating test protocol data units, and multiple reflectors for relaying the test protocol data units along successive segments of a test path in the network. The method generates the test protocol data units at the originator and transmits the test protocol data unit along a test path that includes multiple reflectors. Each reflector relays the test protocol data unit to the next reflector along the test path. Measurements of performance parameters are collected from the multiple reflectors in the test protocol data unit by inserting timestamps into the test protocol data unit at the originator and each of the reflectors to identify the departure and arrival times for each test protocol data unit at the originator and each of the reflectors in both the downstream and upstream directions along the test path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/927,328, filed Mar. 21, 2018 now allowed, which is a continuation ofU.S. patent application Ser. No. 14/557,102, filed Jul. 24, 2012, nowU.S. Pat. No. 9,960,982, which incorporates by reference in its entiretythe following application, which has the same filing date as the presentapplication: “Automatic Setup of Reflector Instances,” by Hansson,Hagsand and Wallman, U.S. patent application Ser. No. 13/557,138, nowU.S. Pat. No. 8,711,708.

FIELD OF THE INVENTION

Multi-hop Reflector Sessions in the context of an Ethernet OperationsAdministration and Maintenance (OAM) framework.

BACKGROUND OF THE INVENTION

For many years, Ethernet has been used as a LAN (Local Area Network)technology, and enterprises have managed these networks with the use ofInternet protocols such as Simple Network Management Protocol (SNMP),ICMP Echo (or IP Ping), IP Traceroute, and Cisco Unidirectional LinkDetection Protocol (UDLD). EOAM (Ethernet Operations Administration andMaintenance) is a set of protocols for installing, monitoring, andtroubleshooting MANs (Metropolitan Area Network) and WANs (Wide Areanetwork). The use of Ethernet as a networking technology has created theneed for a new set of OAM protocols since there are now large andcomplex networks with a wide user base that involves different operatorsproviding end-to-end services.

The IETF (Internet Engineering Task Force) develops and promotesInternet standards. The One-way Active Measurement Protocol [RFC4656](OWAMP) provides a common protocol for measuring one-way metrics betweennetwork devices. OWAMP can be used bi-directionally to measure one-waymetrics in both directions between two network elements. However, itdoes not accommodate round-trip or two-way measurements.

Two-Way Active Measurement Protocol (TWAMP) [RFC5357] provides astandards-based method for measuring the round-trip IP performance(packet loss, delay and jitter) between two devices. TWAMP uses themethodology and architecture of One-Way Active Measurement Protocol(OWAMP) to define a way to measure two-way or round-trip metrics.

There are four logical entities in TWAMP: the Control-Client, theSession-Sender, the Server, and the Session-Reflector. TheControl-Client and Session-Sender are typically implemented in onephysical device (the “Client”) and the Server and Session-Reflector in asecond physical device (the “Server”) with which the two-waymeasurements are being performed.

The Control-Client and Server establish a TCP (Transmission ControlProtocol) connection and exchange TWAMP-Control messages over thisconnection. When the Control-Client wants to start testing, the Clientcommunicates the test parameters to the Server. If the Server agrees toconduct the described tests, the test begins as soon as the client sendsa Start-Session message. As part of a test, the Session-Sender sends astream of UDP-based (User Datagram Protocol) test packets to theSession-Reflector, and the Session-Reflector responds to each receivedpacket with a response UDP-based test packet. When the Session-Senderreceives the response packets from the Session-Reflector, theinformation is used to calculate two-way delay, packet loss, and packetdelay variation between the two devices.

The ITU (International Telecommunication Union) is the United Nationsspecialized agency for information and communication technologies(ICTs). ITU standards (called Recommendations) are fundamental to theoperation of ICT networks. ITU-T Y.1731 performance monitoring providesstandards-based Ethernet performance monitoring that encompasses themeasurement of Ethernet frame delay, frame delay variation, and frameloss and throughput.

IEEE 802.1ag IEEE Standard for Local and Metropolitan Area NetworksVirtual Bridged Local Area Networks Amendment 5: Connectivity FaultManagement is a standard defined by IEEE (Institute of Electrical andElectronics Engineers). It defines protocols and practices for OAM forpaths through bridges and local area networks (LANs). It is largelyidentical with ITU-T Recommendation Y.1731. The standard:

-   -   Defines maintenance domains, their constituent maintenance        points, and the managed objects required to create and        administer them.    -   Defines the relationship between maintenance domains and the        services offered by VLAN-aware bridges and provider bridges.    -   Describes the protocols and procedures used by maintenance        points to maintain and diagnose connectivity faults within a        maintenance domain.    -   Provides means for future expansion of the capabilities of        maintenance points and their protocols.

ITU Y.1731 and similar OAM standards (including but not limited toTWAMP) require an explicit negotiation between the Originator (Client)and the Reflector (Session-Reflector) to establish a unique FlowIdentifier. This approach prevents a Test PDU (protocol data unit) frombeing processed by a multitude of Reflectors downstream from anOriginator, as illustrated in FIG. 1.

Due to the need to explicitly generate different OAM sessions (one perpair of Originator and Reflector) in the current state of the art, it isnot possible to generate a Test PDU from an Originator that can collectmeasurements from more than one Reflector at a time along a test path,even though the Test PDU may traverse said Reflectors in order to reacha remote Reflector.

FIGS. 2-4 are from the ITU Y.1564 standard and are used to illustratethe need for delay and other measurements needed to qualify an Ethernetcircuit at installation. FIG. 2, from ITU Y.1563, illustrates thelayered nature of the performance of the Ethernet service. This networkis comprised of connection-oriented or connectionless links that areconnected to bridges that will process the Ethernet Layer inside thenetwork. Each time an Ethernet frame is going through an Ethernet layer,it will be processed for integrity and sent to the next bridge through aLower Layer (LL) connection. Lower Layers are based on multipletechnologies, for example, SDH, OTN, PDH, MPLS, ATM and ETY. Theperformance of all Ethernet Layers and Lower Layers will impact theend-to-end performance of the network used to deliver services.

Higher layers may be used to enable end-to-end communications. Upperlayers may include protocols like IP, MPLS and Ethernet that allow agreater scalability for network deployment. Other protocols, like TCP,provide the capability to retransmit frames should a frame loss occur.Unfortunately, two of the drawbacks of TCP are added delay in thetransmission of user information, and the possible limitation of maximumadvertised window size and interaction with the bandwidth-delay productand flow control interaction with loss and delay of the EthernetService. The embodiment is able to perform the requested measurementindependently from the fact that the links (or Lower Layer—LL) used tocarry the Ethernet Virtual Circuits (EVC) may operate at Layer 2 orLayer 3.

FIG. 3, taken from ITU Y.1564, provides a simple example of Ethernetservice areas and is referred to as an Ethernet service activationmeasurement. The goal of the test is to verify the configuration andperformance of Ethernet-based services. The test verifies EthernetService Attributes including Committed Information Rate (CIR), ExcessInformation Rate (EIR) and other attributes. This shows the differentportions of a network that support an Ethernet service instance.

It is further shown that the UNI reference point occurs in the middle ofthe access link, or more precisely that the UNI is a reference pointwhose functionality is split into customer (UNI-C) and network (UNI-N)components. From a service provider's perspective, they need to deliverservices from UNI-C to UNI-C and it is from this perspective that thetest methodology was created.

The CE (Customer Equipment) and the operator's network exchange serviceframes across the UNI, a service frame is an Ethernet frame transmittedacross the UNI toward the Service Provider (called ingress serviceframe) or an Ethernet frame transmitted across the UNI towards the CE(called an egress service frame). Many services run on each UNI. Theyare qualified by their attributes:

-   -   Connection type    -   Traffic parameters: QoS (including VLAN information), traffic        type (data vs. management), etc.    -   Bandwidth profile    -   Performance criteria: FD, FDV, Frame Loss ratio, availability,        etc.

From this, it is easy to see that an Ethernet Virtual Circuit mayactually span multiple transport networks at Layer 2 or Layer 3. Thiscreates challenges to efficiently measure delays and packet loss withtraditional methods. The performance measurements can only be takenoutside of the inner boundaries of the Transport Operator Network.

FIG. 4, from ITU-T y.1563, illustrates how Measurement Points (MP) aretypically found at the boundaries between different Lower Layers used tosupport the EVC. The positioning of these MPs (or Reflectors) iscritical to obtain adequate measurements. As per the above diagram, a2-way delay measurement is typically taken from the SRC to the DST andback to the SRC and does not provide detailed delay information for eachExchange Link (or Lower Layer). The performance measurements can only betaken outside of the inner boundaries of the Network Section where MPsare addressable for the purpose of performance measurements.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a method is provided for measuringand reporting performance parameters in a network having at least oneoriginator for generating test protocol data units, and multiplereflectors for relaying the test protocol data units along successivesegments of a test path in the network. The method generates the testprotocol data units at the originator and transmits the test protocoldata unit along a test path that includes multiple reflectors. Eachreflector relays the test protocol data unit to the next reflector alongthe test path. Measurements of performance parameters are collected fromthe multiple reflectors in the test protocol data unit by insertingtimestamps into the test protocol data unit at the originator and eachof the reflectors. The timestamps identify the times when the testprotocol data unit (1) departs from the originator and (2) arrives atand departs from each of the reflectors in both the downstream andupstream directions along the test path.

In one implementation, each of the reflectors is configured with theaddressing information of the next reflector in the test path, and theaddressing information is used to relay the test protocol data unit tothe next reflector. Each reflector is configured with that reflector'sown addressing information for use in receiving the test protocol datapacket from the next reflector during the transmission of the testprotocol data packet from the last reflector back to the originator.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings.

FIG. 1 is a diagrammatic illustration of a test path from an Originatorto multiple Reflectors in an Ethernet.

FIG. 2 is an illustration of the layered structure of the performance ofan Ethernet service, from ITU Y.1563.

FIG. 3 is an example of an Ethernet service activation measurement, fromITU Y.1564.

FIG. 4 is an illustration of the location of Measurement Points (MP) inan Ethernet, from ITU Y.1563.

FIG. 5 is a diagrammatic illustration of where the timestamps aregenerated for 2-way loopback measurements across multiple Reflectors.

FIG. 6 is the ITU Y.1731 Vendor Specific OAM PDU (ETH-VSP).

FIG. 7 is a table of all the PDU fields set by the Originator.

FIG. 8 illustrates the extensions to the format of the STREAM DataType-Length-Value (TLV).

FIG. 9 illustrates the generated and extended Stream Data TLV by theOriginator.

FIG. 10 illustrates the generated and extended Stream Data TLV when usedby a Reflector.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

Although the invention will be described in connection with certainpreferred embodiments, it will be understood that the invention is notlimited to those particular embodiments. On the contrary, the inventionis intended to cover all alternatives, modifications, and equivalentarrangements as may be included within the spirit and scope of theinvention as defined by the appended claims.

The embodiment operates in the context of the need for a framework thatallows for performance measurements as defined in standards such asITU-T Y.1731, IETF RFC 5357 (TWAMP) and IEEE 802.1ag. These standardsall rely on the notion of an Originator (or Session-Sender) thatgenerates test traffic toward a Reflector (or Session-Reflector), where2-way measurements require that the Reflector returns (or reflects) thetest traffic toward the Originator.

These standards allow efficient delay and packet loss measurements via abi-directional measurement function, i.e. 2×OneWay, for switched Layer 2networks, with the capability to measure and report all required metrics(delay, jitter, loss, reorder, etc) for both directions (uplink anddownlink) to state the performance of the network.

The Ethernet OAM framework defines a number of functions forconnectivity verification as well as performance monitoring. Thisembodiment focuses on two of these functions, Ethernet Loopback (ETH-LB)and two-way Frame Delay Measurement (ETH-DM). Both functions arebi-directional, i.e. the Originator will send one or more measurementframes to a Reflector, which sends the measurement frames back (afterprocessing and swapping of MAC addresses, etc) to the Originator.

In ETH-LB, all measured and reported metrics (delay, jitter and framestatistics) are based on two-way measures.

When measuring ETH-DM Delay and jitter (delay variation) the DMM/DMR(Delay Measurement Message/Delay Measurement Reply) messages areextended to contain a Data TLV (Type-Length-Value) with a 32 bitsequence number to measure and report frame statistics (i.e. loss,reorder, duplicated packets) metrics based on two-way measures.

The embodiment is a bi-directional Layer 3 solution with the capabilityto measure and report the metrics mentioned above for both directions. A2×OneWay session consists of an Originator and a Reflector.

When multiple Reflectors are set downstream from an Originator, theOriginator needs to explicitly generate Test PDUs directly toward eachReflector in order to obtain 2-way delay and packet loss measurements.In order to reduce the test traffic and to collect measurements moreefficiently and within a better controlled window of time, there is aneed to generate Test PDUs that can traverse multiple Reflectors andcollect detailed measurements.

The ability to generate a single Test PDU (or a sequence of Test PDU)addressed to the first Reflector which will then relay the Test PDU to anext Reflector downstream which may also relay the Test PDU downstreamuntil the end of a chain of Reflectors and then back upstream (throughthe chain of Reflectors) all the way back to the Originator is highlydesirable. This helps to significantly reduce the test traffic whilecollecting measurements related to the same Test PDU to improve thecorrelation of the measurements.

This embodiment does not require the explicit setup of an “OAM session”between the Originator and the Reflector. The required Flow Identifierto uniquely identify one of potentially multiple OAM sessions isautomatically generated by the Reflector. This method not onlysimplifies the operation of the pair of Originator-Reflector, it alsoallows a Reflector to relay the Test PDU downstream to another Reflectorto extend the range of the measurements obtained by a single 2×OneWayTest PDU to better correlate the overall operation of a network at aspecific point in time. By having each Reflector insert specifictimestamp markers in the downstream direction (away from the Originatorand beyond the initial Reflector in the test path) and then on theupstream direction (for the return path toward the Originator) it ispossible to obtain detailed delay and packet loss measurements for eachLower Layer connection where a Reflector is present while increasing thecorrelation of the measurements since they are all relative to the sameoriginal Test PDU.

By having each Reflector in a test path inserting a Stream Data TLV tohold their specific measurements and updating the meaning of theTimestamps as defined in ITU Y.1731 (and related standards), it ispossible to collect measurements from multiple Reflectors along a testpath by generating a single Test PDU from an Originator. The amount oftest PDU generated by the Originator is significantly reduced whilecollecting more measurements from a single PDU from the Originator. Theadditional measurements from intermediate Reflector hops significantlyenhances the information available to more precisely identify delaysand/or packet loss on specific segments (between a pair of Reflectorunits).

In this embodiment, the initiator of a 2-way delay measurement is calledan Originator (Session-Sender) and the Reflector (Session-Reflector)replies to the 2-way delay measurement requests.

FIG. 5 illustrates where the timestamps (105, 106, 107, 108, 109, 110,111, 112, 113, 114, 115, 116, 117, 118, 119, 120) are generated for2-way loopback measurements from the Originator 100 across multipleReflectors (101, 102, 103, 104). It is possible to obtain delay andpacket loss measurements from a multitude of Reflectors (101, 102, 103,104) each distant by one hop (although each hop may result into multiplesub-networks or Exchange Links) By leveraging the measurementsaccumulated in the Test PDU (via Stream Data TLVs inserted in thepayload portion of the Test PDU), it is possible for the Originator 100to collect and compute detailed delay and packet loss performancemeasurements. For instance, it is possible to compute the following:T3orig−T0orig=total 2-way delay from Originator (100) all the way toReflector n (104)T1orig−T0orig=1-way delay from Originator (100) to Reflector 1(101)T1R1−T0R1=1-way delay from Reflector 1(101) to Reflector 2(102)T1Rn−T0Rn−1=1-way delay from Reflector n−1(103) to Reflector n(104)T1Rn−T0orig=1-way delay from Originator (100) all the way to Reflectorn(104)T3Rn−1−T2Rn=return delay from Reflector n(104) to Reflector n−1(103)T3R2−T3R1=return delay from Reflector 2(102) to Reflector 1(101)T3R1−T0R1=total 2-way delay from Reflector 1(101) all the way toReflector n(104) and back

One familiar with the state of the art shall be able to computeadditional delay measurement information based on the multipletimestamps accumulated along the test path in the downstream (toward theend Reflector 104) and upstream return test path toward the Originator100.

There are multiple options to allow the Test PDU from the Originator 100toward the Reflector 1 (101) to proceed along the test path acrossmultiple downstream Reflectors (102, 103, 104).

In one implementation, each Reflector (101, 102, 103, 104) is configuredwith the addressing information required to relay the Test PDU to thenext downstream Reflector. Using this approach, each Reflector (101,102, 103, 104) only needs to be configured with information about theReflector directly downstream from it (as per the defined test path).When relaying the Test PDU to the downstream Reflector, the relayingReflector will include its addressing information to be able to receivethe reply from the downstream Reflector.

In another implementation, the Originator 100 addresses the Test PDUdirectly to the last Reflector (104) in the chain of Reflectors (101,102, 103, 104) in the test path, but route to the Reflector 1 (101)along the test path. The intermediate Reflectors (102, 103) operate as aseries of “routers,” with each Reflector inserting its own measurementsin the appropriate Stream Data TLV assigned to it and then relaying theTest PDU to the next Reflector in the test path (downstream or upstreamdirection).

In yet another implementation, the Originator 100 is aware (byconfiguration or via a discovery method) of the list of Reflectors (101,102, 103, 104) along the test path. This allows the Originator 100 topre-fill all of the required Stream Data TLV 300 (one per Reflector 101,102, 103, 104 instance) as part of the payload of the Test PDU. An indexfield is incremented by each intermediate Reflector 101, 102, 103, 104to allow it to identify which Stream Data TLV 300 is assigned to it. Theaddressing information of the next/downstream Reflector is also includedin the Test PDU by the Originator 100. This information is then used byan intermediate Reflector (101, 102) to relay the Test PDU to the nextReflector in the downstream direction and up toward the previousReflector in the upstream/return path direction.

In another implementation, the Test PDU is addressed to the lastReflector 104 along the test path. Each intermediate Reflector operatesin a Promiscuous Mode and peeks into the Test PDU to insert its ownmeasurements in the appropriate Stream Data TLV before relaying the TestPDU to the next Reflector along the test path in the downstream orupstream direction (as required).

In another implementation, each intermediate Reflector generates adirect reply to the Originator 100 as if the Test PDU had been directlyreceived from that Originator 100. This approach can generate the samelevel of measurements, but care is needed since the higher number ofreplies generated toward the Originator could overflow the Originator orimpact the performance of user data when used in service rather thanduring the Service Activation phase.

When there are multiple (downlink) Reflectors behind a given Reflector,for instance in a star topology, the Originator 100 is expected tohandle each potential branch of the star topology as a different testpath and initiate a 2-way measurement for each possible pathindependently of the other.

Depending on the specific definition of the various standards where thepresent embodiment applies, there may be a need to extend the encodingof the test PDUs if there is not native support for at least 3timestamps.

An example of a standard that support the use of TLV to carry at least 3timestamps is the ITU Y.1731 standard. In order to carry themeasurements from each Reflector visited along the test path, the ITUY.1731 protocol provides an extensible encoding via the concept ofvendor specific OAM-PDU (ETH-VSP). A Stream Data TLV is added to theETH-VSP encoding for each visited Reflector to carry the 2-waymeasurement test defined in this disclosure. The timestamps (T0 to T3)use the timestamp format defined in IEEE 1588-2004. The Stream Data TLVfor ETH-VSP has been assigned MType=209.

FIG. 6 illustrates the ITU Y.1731 Vendor Specific OAM PDU (ETH-VSP).

FIG. 7 is a table of all the PDU fields set by the Originator 100 whichcannot not be modified by the Reflector (101, 102, 103, 104), except theOpCode field 302. The Stream Data TLV 300 is extended for thisembodiment.

FIG. 8 illustrates the extensions to the format of the Stream Data TLV300. The Stream Data TLV 300 shall be extended to include a uniqueidentifier (or index) for each Reflector (101, 102, 103, 104) along thetest path. The Reserved Field 400 is used to hold a unique Reflectoridentifier.

Furthermore, each Stream Data TLV 300 in the payload of the Test PDUshall include the 4 timestamps needed to gather the necessary delaymeasurements from each Reflector in the test path.

FIG. 9 illustrates the generated and extended Stream Data TLV by theOriginator 100.

FIG. 10 illustrates the generated and extended Stream Data TLV 300 whenused by the Reflector (101, 102, 103, 104) in reply to a test PDUreceived from the Originator 100 (directly or via an upstreamReflector).

When a standard, such as RFC5357 TWAMP, does not provide native supportfor at least 3 timestamps per reflector hop (such as multiple TLV),there is a need to extend the said protocol. An implementation is toleverage the unused portion (or filler) of the Test Packet to hold astructure that can store the at least 4 timestamps and, uplink anddownlink sequence numbers for each Reflector hop. Such a structure canalso be extended to fundamentally include the additional informationdefined in the Data Stream TLV 300 in FIG. 6 MEG Level including but notlimited to: received and transmitted (600, 601), P-Bit received andtransmitted (602,203), etc. The TLV encoding shown as part of animplementation compatible with ITU Y.1731 could be used or any othervariation well known to those familiar with the art. The selectedimplementation picks a Test PDU size large enough to hold the SequenceNumbers (401, 402) and Timestamps (403, 404, 405, 406, 407, 408, 409,410) information for each Reflector hop without exceeding the maximumPDU size supported by the Service OAM standard and the underlying Layer2 and/or Layer 3 networks or network segments.

To identify the TLV to use for a specific Reflector (101, 102, 103,104), when a Reflector (101, 102, 103, 104) receives a Test PDU with theOpCode 302 set to VSM (51), the Reflector searches the set of StreamData TLV 300 in the payload of the Test PDU to determine whether thereis already a Stream Data TLV 300 that was generated by the Originator100 for this Reflector (101, 102, 103, 104). If the Stream Data TLV 300is not found, the Reflector (101, 102, 103, 104) adds a Stream Data TLV300 after the last Stream Data TLV 300 found and moves the End TLV 301marker after the newly inserted Stream Data TLV 300. The Reflector (101,102, 103, 104) sets the Reserved/Reflector ID field 500 to the unique IDassigned to the Reflector (101, 102, 103, 104).

The Reflector then sets the T0 and T1 timestamps (105, 106, 107, 108,109, 110, 111, 112).

If there is another downstream Reflector, the Reflector relays the TestPDU to the next Reflector.

Otherwise, if the Reflector is the last one in the chain of Reflectorsalong the test path (104), it changes the OpCode field 302 to VSR (50)and sets the T2 and T3 timestamps (120, 119). For the Reflector at theend of the test path, the T3 timestamp 119 is set to 0. Once the StreamData TLV 300 is updated, the VSR is returned to the upstream Stream DataTLV 300 toward the Originator 100.

If a Reflector 101, 102, 103, 104 receives a Test PDU with the OpCode302 already set to VSR, it retrieves the Stream Data TLV 300 with theReflector ID of the Reflector and then updates the T2 and T3 timestamps(113, 114, 115, 116, 117, 118, 119, 120) before relaying the Test PDUupstream to the previous Reflector or the Originator 100 if there are noupstream Reflectors along the return test path.

If there is no Stream Data TLV 300 found before the one assigned to theReflector, this is an indication that there is no other Reflector andthe Test PDU is returned directly to the Originator 100.

Since a Reflector Session is automatically set up, a timeout mechanismis implemented to tear down a Reflector session and free associatedresources whenever Test PDUs are not received from the Originator 100(identified by a unique Flow Identifier) for a pre-determined period oftime (typically in the order of 10 seconds). Should new Test PDUs bereceived from the same Originator 100 after the expiration of the idletimer, the Reflector (101, 102, 103, 104) automatically generates a newFlow Identifier. A complementary tag is therefore required to indicateto the Originator 100 that a new Reflector Session has beenautomatically set up. This is achieved by an Incarnation Number (IncNum411 in the Stream Data TLV 300) returned by the Reflector (101, 102,103, 104). The IncNum 411 is an unsigned integer value generated from aglobal incarnation counter, and the counter is increased by one (1) eachtime a new IncNum 411 is allocated.IncNum=IncNumCnt;IncNumCnt=IncNumCnt+1;

The above 2-step operation is implemented as an atomic operation toensure the incarnation number counter is increased at the same moment anew IncNum 411 is assigned to a Reflector instance.

The global incarnation number counter is initialized once to a randomnumber at system startup to minimize the probability of reusing the sameIncNum 411 for a Reflector instance after a system restart. Thewrap-around rate of the global incarnation counter depends on thearrival rate of new measurement streams and the re-activation rate ofalready running measurement streams.

In one embodiment, a Reflector (101, 102, 103, 104) compares a newlygenerated IncNum 411 with an older Reflector Session instance, and ifequal, generates a new IncNum 411, to avoid assigning the same IncNum411 to a Reflector Session serving one and the same measurement stream.

The embodiment described is applicable to software-based, HW-based andsmall-form pluggable (SFP) Field Programmable Gate Array (FPGA)Originators and Reflectors. The embodiment also applies to any networkdevice that can be addressed using a layer-2 address (MAC address)and/or a layer-3 address (such as an IP address).

FIG. 5 is a diagrammatic illustration of a system similar to that ofFIG. 4 in which the FPGA is configured as an embedded traffic generator.

FIG. 6 is a diagrammatic illustration of a system similar to that ofFIG. 4 in which the FPGA is configured to perform intelligent loop back.

While particular embodiments and applications of the present inventionhave been illustrated and described, it is to be understood that theinvention is not limited to the precise construction and compositionsdisclosed herein and that various modifications, changes, and variationsmay be apparent from the foregoing descriptions without departing fromthe spirit and scope of the invention as defined in the appended claims.

The invention claimed is:
 1. A method for measuring one or moreperformance parameter relating to a test path of a network, said testpath comprising an originator and multiple reflectors comprising:generating by the originator a test protocol data unit; assigning aunique flow identifier uniquely identifying each reflector in the testpath; collecting measurements of said performance parameters at each ofsaid multiple reflectors; inserting said collected measurements and atimestamp in said test protocol data unit associated with said uniqueflow identifier corresponding to the reflector in which that measurementwas collected; relaying by each reflector said test protocol data unitto a subsequent reflector along said test path until a last reflector inthe test path is reached; transmitting by each of said reflectors saidmeasurements of performance parameters directly back to said originator;wherein the last reflector in the test path sends the test protocol dataunit to the originator for processing.
 2. The method of claim 1, inwhich said performance parameters include delay.
 3. The method of claim1, in which said analyzing comprises computing a total two-way delaymeasurement of said test data protocol unit's transit along said testpath from said originator to the last reflector, and back from the lastreflector to said originator, based on said timestamps inserted in thetest protocol data unit in both the downstream and upstream directions.4. The method of claim 3, in which said one of said multiple reflectorsretrieves a reverse address from said test protocol data unit andinserts a reverse address for said subsequent reflector along said testpath, said one of said multiple reflectors utilizing said reverseaddress to return said test protocol data unit in the reverse directionalong said test path.
 5. The method of claim 1, in which each of saidreflectors is configured with the addressing information of the nextreflector in said test path, and said addressing information is used torelay the test protocol data unit to said next reflector.
 6. The methodof claim 1 in which said performance parameters are stored in a testdata protocol unit that stores at least three timestamp values, and ifsaid test data protocol unit does not store at least three timestampvalues, said test data protocol unit is expanded to store at least threetimestamp values.
 7. The method of claim 1, in which said originatorpre-fills said test data protocol unit with each reflector's addressinginformation corresponding to the unique flow identifier and saidaddressing information is used to relay the test data protocol unit tothe next reflector.
 8. A system for measuring one or more performanceparameter relating to a test path of a network, said test pathcomprising an originator and multiple reflectors comprising: a testprotocol data unit generated by the originator and transmitted to afirst reflector along the test path; a unique flow identifier uniquelyidentifying each reflector in the test path; a timestamp inserted insaid test protocol data unit associated with said unique flow identifierof the reflector; a collection of measurements of said performanceparameters at each of said multiple reflectors and a timestamp insertedin said test protocol data unit associated with said unique flowidentifier corresponding to the reflector; said test protocol data unitis relayed by one reflector to a subsequent reflector downstream in thetest path until a last reflector in the test path is reached; and thelast reflector in the test path sends the test protocol data unit to theoriginator for processing; and wherein said each of said multiplereflectors transmit said measurements of performance parameters directlyback to said originator.
 9. The system of claim 8, in which saidperformance parameters include delay.
 10. The system of claim 8, furthercomprising a total two-way delay measurement of said test data protocolunit's transit computed along said test path from said originator to thelast reflector, and back from the last reflector to said originator,based on said timestamps inserted in the test protocol data unit in boththe downstream and upstream directions.
 11. The system of claim 8, inwhich each of said reflectors is configured with the addressinginformation of the next reflector in said test path, and said addressinginformation is used to relay the test protocol data unit to said nextreflector.
 12. The system of claim 8, in which said one of said multiplereflectors retrieves a reverse address from said test protocol data unitand inserts a reverse address for said subsequent reflector along saidtest path, said one of said multiple reflectors utilizing said reverseaddress to return said test protocol data unit in the reverse directionalong said test path.
 13. The system of claim 8, in which saidperformance parameters are stored in a test data protocol unit thatstores at least three timestamp values, and if said test data protocolunit does not store at least three timestamp values, said test dataprotocol unit is expanded to store at least three timestamp values. 14.The system of claim 8, in which said originator pre-fills said test dataprotocol unit with each reflector's addressing information correspondingto the unique flow identifier, and said addressing information is usedto relay the test data protocol unit to the next reflector.